1. Field of the Invention
The present invention relates to a semiconductor device having an antifuse element.
2. Description of Related Art
A large-capacity semiconductor memory, in particular a DRAM (Dynamic Random Access Memory) is provided with a redundant memory for improvement of yield, so that when there exists a defective memory cell, the column or word containing the defective memory cell is replaced with the redundant memory. The replacement with the redundant memory is carried out by writing address information indicating the column or word to be replaced in a ROM (Read Only Memory).
Fuse ROMs have been widely used as this type of ROMs. A fuse ROM includes a plurality of fuse elements, and information is written by selectively cutting the fuse elements.
The cutting of the fuse elements is carried out with the use of a laser beam. Therefore, the employment of the fuse ROMs involves various restrictions. For example, a large sized laser irradiation apparatus is required, and the writing of information is allowed only in the wafer stage (before the assembly stage) of the manufacturing process.
In order to overcome these problems, there have recently been proposed ROMs employing electrically breakable antifuse elements. An antifuse element has a configuration basically identical to that of a capacitor. Specifically, an open circuit is established between the opposite terminals of the antifuse element in its unbroken state, whereas a short circuit is established between the opposite terminals of the antifuse element when a dielectric layer is broken by applying a high voltage between the terminals. Information is recorded according to the conductive and non-conductive states of the antifuse element.
The antifuse element can be downsized compared to a fuse element, resulting in reduction of the occupying area. Additionally, the antifuse element enables writing (breakdown) by means of a high voltage generated within the semiconductor device, eliminating the need of a large-scaled laser irradiation apparatus. Further, the antifuse element enables writing even after completion of the assembly process, contributing to further improvement of the yield. A semiconductor device having such an antifuse element is described for example in Japanese Laid-Open Patent Publication No. 2008-47215 (Patent Document 1). More specifically, Patent Document 1 describes a technique in which there is stored in an antifuse element various information, including information on defective cells to be replaced with redundant cells, information relating to level adjustment of an internal power generating circuit, and information relating to impedance adjustment of an input/output circuit.